Controlled magnetic roughness in a multilayer that has been patterned using a nanosphere array

The micromagnetic structure of an antiferromagnetically exchange-coupled multilayer constrained by a periodic in-plane structure has been quantified using polarized-neutron reflectometry. The pattern was realized through nanosphere lithography. The fabrication of the patterned array introduces a significant deviation in the in-plane magnetization direction near to and at the surface of the heterostructure but does not significantly perturb the domain structure. The characteristic length scale of this magnetic roughening is shown to be driven by the feature size. The roughening is not observable by conventional magnetometry techniques but is confirmed by micromagnetic simulation. The combination of scattering techniques and numerical simulation provides a powerful tool to study the subtle interlayer and intralayer ordering in patterned magnetic heterostructures.